Metal working



Patented Mar. 6, 1934 UNITED STATES METAL WORKING Nikolaus Bregger, Vienna, Austria No Drawing. Application September 30, 1931, s sn No. 566,175. In Austria October 17,

Claims.

This invention relates in particular to a process for drawing, rolling, or pressing metal such as iron and steel in the manufacture of tubes, wire, sheet, articles made of sheet metal, and the 5 like. Such metals, while capable of being drawn or Worked cold to a limited extent, require this to be accomplished by a series of successive steps, each involving pickling, annealing, and reworking, Where the elongation or reduction is extenl0 sive.

It has been proposed in the past to coat the steel with lead and zinc and other metals having a low coefficient of friction, and then to apply successive drawing or rolling operations; but even in such cases the amount of drawing or reduction which is possible Without injury to the metal and Without intervening annealing stages is strictly limited.

The main object of the present invention is to provide a process of working metal, in particular iron and steel, in the cold state by which the said metal can be subjected to a large number of reducing stages Without the necessity for intervening annealing and pickling operations, and

without injury to the metal. The enormous practical advantages of such a process will become more apparent in the course of the following specification.

According to my invention the material to be prepared, for instance a steel tube, is first cleaned to remove all scale, oil, etc., e. g. by submersion in a pickling solution of the usual character. Next, the surface of the pickled steel is materially roughened or superficially corroded, this being preferably accomplished by the action of an acid or acid solution continued to a sufficient extent to leave the surface of the steel very rough and spongy and yet perfectly clean. This roughened stock is then submerged in a bath of anti-friction metal, preferably after having taken the precautionary measures sometimes used When a solid metal is brought into contact with a moltenone, and preferably at a temperature considerably above the melting point of the bath, in which the stock is allowed to remain for some time. The stock is then removed from the bath of metal and allowed to cool, thus leaving a very thin coating of the anti-friction metal closely adhering to the stock and filling up all of the superficial interstices.

I have found that stock thus treated can be subjected to a very large number of consecutive cold drawing or rolling passes Without any necessity of intervening annealing or pickling op- 0' erations. In fact, steel tubes treated in this way have been subjected to as many as twelve passes Without injury to the stock. Samples subjected to microscopic examination indicate that the preliminary treatment so roughens the surface that the molten bath is able to permanently anchor itself within the minute surface spaces, almost if not quite to the point of forming an alloy with the iron, although it is not generally considered that such anti-friction metals will alloy with iron or steel.

It will be understood that the pickling and roughening operations may also be accomplished by means of a single bath consisting of a suitable etching liquid, say an acid or a mixture of one or more acids or other substances, this etching liquid first acting as a pickling bath by cleaning the surface of the stock and removing scale therefrom, and then as a roughening bath by corroding the cleaned surface. The pickling and roughening baths used in my invention may be either cold or hot.

The roughening bath may consist of a strong acid, such as hydrochloric acid or sulphuric acid, or of a mixture of acids. For instance, four parts of water and one part of ninety percent hydrochloric acid or one part of sixty six percent sulphuric acid, respectively, constitute a suitable roughening bath. Also a less concentrated bath consisting of say two parts of water and one part of thirty three percent hydrochloric acid may be of use in many cases for corroding the surface of the stock. The stock is left in the roughening bath for a sufficient length of time, which must be determined exteprimentally for a given composition of stock, the duration being dependent largely upon the hardness and composition of the stock to be treated. The harder the stock the more concentrated should be the acid solution for a given period of submersion, or the longer should be the submersion with a solution of a given concentration. High carbon steels may require from ten to fifteen minutes submersion, while a low carbon or soft steel should not require more than from five to ten minutes treatment. Hard chrome nickel and similar hard steel alloys may require even fifteen to twentyfive minutes treatment.

The etching carried out according to my invention has the specific purpose of roughening the surface which has been cleaned and smoothed by the pickling bath, or in other words, of permitting an etching liquid to form surface depressions or cavities by eating into or corroding the surface. These depressions or cavities penetrate the surface to a greater or less extent, de-

pending upon the nature of the etching liquid and the duration of the treatment.

The chemical reaction occurring on submersion of the work-piece in the etching bath can be very accurately observed, because of the fact that this reaction is manifested by bubbles of gas rising to the surface of the bath. Having once determined the duration of the treatment to produce a certain degree of roughness on a given material in a certain etching bath, it is merely necessary to observe the time from. the moment bubbles form on the surface until the termination of the treatment, in order to have an accurate measure for the treatment of all subsequent work-pieces of the same type.

With pickling the formation of bubbles indicates that the pickling process is finished. In the known process for preparing a stock for drawing the stock is subjected to the action of a pickling bath only for the purpose of cleaning, preparatory to the application of a coating of anti-friction metal, so that the pickling liquid employed is not such as to be capable of etching the material of the stock itself. The appearance of bubbles in the pickling bath has thus hitherto been taken as a signal for the immediate removal of the stock from the bath. In the present process, on the other hand, bubble formation indicates the starting of the etching process.

Before submerging the stock in the molten bath of antifriction metal precautionary measures may be inserted, which preferably consist in washing the roughened surface in water, and then dipping the stock in a so-called preliminary bath for the purpose of preventing undesired oxidation of the surface during the following submersion in molten metal. Such preliminary baths are well-known in the art, when a solid metal is to be brought into contact with a molten one, as for instance in the soldering art. A suitable preliminary bath may consist of say four parts of ninety percent hydrochloric acid, from one and four tenths to one and nine tenths parts of ammonium chloride and from one and two tenths to one and eighth tenths parts of zinc dissolved in it. It is to be understood that under circumstances the washing in water or the preliminary bath or both steps may be omitted.

The molten bath consists preferably of lead and tin in proportions which may be varied and will depend largely upon the hardness of the stock. For instance, the harder the stock the larger the tin content of the alloy. For a low carbon steel in the tin content may be say five percent of the alloy, and the lead ninety-five percent. A high carbon steel may require ten percent of tin and ninety percent of lead. With chrome nickel steel and exceptionally hard stock the tin may be increased even to twenty-five percent and the lead correspondingly decreased. In some cases lead and tin may be used for the coating in a pure state, i. e. without alloying same. Other soft metals e. g. antimony or bismuth, may replace the lead or tin in the molten bath and in the coating. It will be understood that the aptitude of metals or alloys for the coating depends on their softness, as the coating has to be softer than the stock.

It is important that the stock be left submerged in the coating bath for a sufiicient length of time to permit the stock to acquire a temperature of at least 400 C. or approximately to that of the bath. With a moderately soft steel the temperature may run as high as 420 or 430 C. At such eagues temperatures considerable above the melting point of lead and of tin, these metals tend to unite with the iron or steel much more closely than at lower temperatures, in fact the solubility of iron in lead and tin increases at higher temperatures. With some metals the temperature can be as low as 360 C. and with others as high as 500 C., the temperature to be chosen also depending on the desired thicknessof the coating. Preferably the coating should be very thin, and accordingly, the temperature of the molten bath raised to the higher values.

The time necessary for the stock to reach these temperatures will, of course, depend upon the bulk of the stock and of the alloy, as well as upon the composition of the steel and upon the composition and temperature of the alloy. When the requisite temperature has been reached the stock is then removed from the metal bath, and is ready to be drawn or rolled in any desired number of consecutive passes, without intermediate annealing or pickling operations.

The metal coating penetrates into all the cavities in the surface of the work-piece, thereby preventing the metal coating from being entirely or partly scraped off during the first and subsequent passes.

Only a thin, film-like coating of the anti-friction metal is necessary. Such a coating anchored or alloyed with the surface of the stock remains attached and will not peel or flake off in the subsequent working.

As an example I may state that steel tubing of 42 mm. outside diameter and 4.4 mm. thickness of wall, prepared in the above-described manner, has been subjected to seven consecutive cold drawing operations of the usual type with the resultant final dimensions of 25 mm. outside diameter and 1.4 mm. thickness of wall. It should not, however, be assumed that this result represents the limit of possible achievement, because I have found it possible to subject such material to a number of additional passes without intermediate treatment and without damage to the material. I

Similar advantages may be obtained by treating strips and bars of metal in the manner described above. In fact, the profile of the stock to be treated is not material to my invention.

Examination of a cross-section of stock treated according to the present invention shows that the anti-friction coating has penetrated into the cavities in the surface of the stock, and remains firmly adhering through all the passes, each pass appearing to wipe off the coating from the outside of the extreme points of the roughened steel, leaving the lubricating metal all around it and in its surface for lubrication in the subsequent passes.

The cavities formed by the etching thus constitute reservoirs of the anti-friction metal which become available gradually as the surface is drawn out. This is very important since the superficial area of the piece increases with each pass.

While I prefer to roughen the surface by chemical action, as described, it is possible that some of the advantages of my complete process may be obtained by roughening in some other manher, such as mechanically, e. g. by sandblasting.

It will be understood that the various cold rolling or drawing steps may be accomplished by means of the usual type of commercial apparatus, and that the stock will be handled in these mechanical operations in the usual way. For instance, in drawing tubes any convenient type of draw bench may be employed, at the usual speed of operation, with the usual wool fat or other lubricant, and with standard dies and mandrels. The stock thus treated will show smooth surfaces inside as well as outside.

The advantages of this process while more or less obvious are actually of enormous commercial importance. The elimination of the various annealing and pickling operations which are necessary with existing processes reduces the time required enormously. In fact, two days time can be saved for each pass, and the total labour costs may be reduced by as much as sixty percent.

Obviously, there is a substantial saving in equipment and plant required for carrying out the operations. As the time required for the complete process is greatly reduced, it is obvious that the capital investment and inventory of raw material and semi-finished material can be greatly reduced.

It should be understood, of course, that the stock, after the completion of the various steps of my improved process, may be annealed, machined, plated, and otherwise treated as is customary.

In case of the surfaceof the stock to be prepared being already clean and free of scale the pickling step which precedes the roughenlng of the surface may be omitted.

The omission of the intervening annealing and pickling stages saves a great amount of fuel and chemicals, as well as labor.

I claim:

1. The method of manufacturing iron or steel articles from a work piece by a number of successive elongation treatments or passes without any preliminary or intermediate annealing and without pickling or fresh coating of the piece between the passes, said method consisting in first removing scale and other impurities from the surface of the work piece by a pickling treatment, then converting the cleaned metallic surface into a rough and spongy condition by corroding the same by means of an etching substance, then coating the surface with a thin film-like layer of anti-friction material penetrating into and filling up all the cavities in the spongy surface, and finally subjecting the work piece to several successive elongation passes to reduce it to the required cross sectional configuration.

2. In the process of manufacturing articles from a metallic work piece by several successive elongation treatments or passes without any intermediate annealing or pickling or fresh coating of the piece between the passes, the preparatory steps which are preliminary to the first elongation treatment and produce reservoirs of anti-friction material within the metallic surface of the work piece, said steps excluding any annealing treatment of the piece and comprising first removing scale and other impurities from the surface of the piece, then corroding the cleaned metallic surface by treating it with a strongly etching substance sufiiciently to form multitudinous small cavities within the surface and to convert the latter into a rough and spongy condition, and finally filling up the said cavities with anti-friction material and coating the surface of the of the work piece with a thin film-like layer of the same material, the filled cavities thus constituting reservoirs of the anti-friction material which become available gradually as the surface is worked by elongations.

3. In the process of manufacturing iron or steel articles from a work piece by several successive elongation treatments or passes without any intermediate annealing or pickling or fresh coat: s; of the piece between the passes, the preparatory steps which are preliminary to the-first elongation treatment and produce reservoirs of anti-friction material within the metallic surface of the work piece, said steps excluding any annealing treatment of the piece and comprising first dipping the piece into an etching bath and leaving it therein until the surface of the piece has con verted into a pure metallic state having a spongy structure, and thenfilling up the cavities in the spongy surface with anti-friction material and coating said surface with a thin film-like layer of the same material, whereby the filled cavities constitute reservoirs of the anti-friction material which become available gradually as the surface is worked by elongations.

4. In the process of manufacturing articles from a metallic work piece by several successive elongation treatments or passes without any intermediate annealing or pickling or fresh coating of the piece between the passes, the preparatory steps which are preliminary to the first elongation treatment and produce reservoirs of anti-friction material within the metallic surface of the work piece, said steps excluding any annealing treatment of the piece and comprising first dipping the piece into a strong acid and leaving it therein until the surface of the piece has converted into a pure metallic state having a spongy structure, then submergingthe piece in a bath of a molten'anti-friction metal having a temperature materially higher than the melting point of said metal, and finally removing the work piece from this bath after a time which is suificient to permit the surface of the piece to acquire the temperature of the bath, whereby this surface is coated only with a very thin film-like layer of anti-friction metal filling up all the cavities in the spongy surface.

5. The method of manufacturing iron or steel articles from a work piece by a number of successive elongation treatments or passes without any preliminary or intermediate annealing and without pickling or fresh coating of the piece between the" passes, said method consisting in first dipping the piece into a strong acid and leaving it therein beyond the formation of bubbles until the surface of the piece has converted into a pure metallic state having a spongy structure, than subjecting the piece to the precautionary treatment well known in the art whenever a solid metal is to be brought into contact with a molten one, then submerging the piece in a bath of a molten anti-friction metal having a temperature materially higher than the melting point of the said metal, then removing the piece from this bath after a time which is suflicient to permit the antifriction of metal of filling up all the cavities in the spongy surface of the piece and of forming a thin film-like coating thereupon, and finally subjecting the coated work piece to several successive elongation passes, to reduce it to the required cross sectional configuration.

6. A semi-manufactured article adapted to be finished by repeated elongation operations or passes without intermediate annealing or pickling, said article consisting of a steel body having a corroded spongy surface containing multitudinous small cavities and of a thin film-like layer of anti-friction material coating said body and filling up the cavities in the spongy surface thereof, the said filled cavities constituting reservoirs of the anti-friction material which become available gradually as the surface is worked by elongations, thus being adapted to prevent the anti-friction material from being entirely scraped off during the passes.

'7. In the process of manufacturing an article from a metallic work piece by several successive elongation treatments or passes without any intermediate annealing or pickling or fresh coating of the piece between the passes, the preparatory steps which are preliminary to the elongation treatment and produce reservoirs of antifriction metal within the surface of the work piece, said steps comprising first dipping the piece into a strong acid solution and leaving it therein while substantial etching takes place and until the surface of the piece has been converted into a state having a spongy structure, then submerging the piece in a bath of molten anti-friction metal having a temperature above the melting point, and leaving the work piece in this bath for a time which is sufiicient to permit the surface of the piece to acquire a temperature at least as high as the melting point and then removing the work piece, whereby the surface is impreghated and coated with a very thin film-like layer of anti-friction metal filling up all the cavities in the spongy surface.

8 In the process of manufacturing an article from a steel work piece by several successive elongation treatments or passes without any intermediate annealing or pickling or fresh coating of the piece between the passes, the preparatory steps which are preliminary to the elongation treatment and produce reservoirs of antifricti0n metal Within the surface of the work piece, said steps comprising first dipping the piece into a strong acid solution and leaving it therein while substantial etching takes place and until the surface of the piece has been converted into a state having a spongy structure, then dipping the piece in a preliminary non-oxidizing solution, then submerging the piece in a bath of molten anti-friction metal having a temperature above the melting point, and leaving the work piece in this bath for a time which is sufficient to permit the surface of the piece to acquire a temperature at least as high as the melting point and then removing the work piece, whereby the surface is impregnated and coated with a very thin film-like layer of anti-friction-metal filling up all the cavities in the spongy surface.

9. In the process of manufacturing an article from a steel work piece by several successive elongation treatments or passes without any intermediate annealing or pickling or fresh coating of the piece between the passes, the preparatory steps which are preliminary to the elongation treatment and produce reservoirs of anti-friction metal within the surface of the work piece, said steps comprising first dipping the piece into a strong acid solution and leaving it therein while substantial etching takes place and until the surface of the piece has been converted into a state having a spongy structure, then sub merging the piece in a bath of molten alloy of tin and lead, the proportions being between 5 and 25% of tin and between 95 and of lead having a temperature above the melting point, and leaving the work piece in this bath for a time which is sufiicient to permit the surface of the piece to acquire a temperature. at least as high as the melting point and then removing the work piece, whereby the surface is impregnated and coated with a very thin film-like layer of antifriction metal filling up all the cavities in the spongy surface.

10. In the process of manufacturing an article from a steel work piece by several successive elongation treatments or passes without any intermediate annealing or pickling or fresh coating of the piece between the passes, the preparatory steps which are preliminary to the elongation treatment and produce reservoirs of anti-friction metal within the surface of the work piece, said steps comprising first dipping the piece into alstrong acid solution and leaving it therein while substantial etching takes place and until the surface of the piece has been converted into a state having a spongy structure, then submerging the piece in a bath of molten metallic alloy having a temperature of approximately 420 C., and leaving the work piece in this bath for a time which is sufficient to permit the surface of the piece to acquire a temperature at least as high as the melting point and then removing the work piece, whereby the surface is impregnated and coated with a very thin film-like layer of antifriction metal filling up all the cavities in the spongy surface.

NIKOLAUS BREGGER. 

